- Use gst_element_send_event() instead of gst_pad_push_event()
- don't zero App structure
- check for pipeline parsing error
- only get vaapisink for property set
This implements a pipleint to recognize difference between ROI and non-ROI.
See comments in this code in detail.
https://bugzilla.gnome.org/show_bug.cgi?id=768248
Signed-off-by: Víctor Manuel Jáquez Leal <vjaquez@igalia.com>